Sensorless Control of Switched Reluctance Machines

ABSTRACT

A control system for a switched reluctance (SR) machine having a rotor and a stator is provided. The control system may include a converter circuit in electrical communication between the stator and a common bus, and a controller configured to monitor a bus voltage of the converter circuit and a phase current of the SR machine. The controller may be configured to determine a phase voltage based on one or more of main pulses and any diagnostic pulses, determine an estimated flux based on the phase voltage and an associated mutual voltage, determine a rotor position based at least partially on the estimated flux, and control the SR machine based on the rotor position and a desired torque.

TECHNICAL FIELD

The present disclosure relates generally to switched reluctancemachines, and more particularly, to sensorless systems and methods forcontrolling switched reluctance machines.

BACKGROUND

An electric machine such as an electrical motor, power generationsystem, genset, or the like, is generally used to convert one form ofenergy into another and may operate in a motoring mode to convertelectrical input into rotational or otherwise mechanical output, oroperate in a generating mode to convert rotational or otherwisemechanical input into electrical output. Among the various types ofmachines available for use with an electric drive, switched reluctance(SR) machines have received great interest for being robust andcost-effective. While currently existing systems and methods forcontrolling such electric machines may provide adequate control, thereis still room for improvement.

Among other factors, proper determination of the position and speed ofthe rotor of the SR machine during relatively low speed operations mayhave significant impacts on overall performance and efficiency. Someconventional control schemes rely on mechanically aligned speed wheelsand sensors to detect and determine the position of the rotor relativeto the stator at machine standstill or low speed operations. However,such sensor-based control schemes typically require costlyimplementations and are susceptible to error. For instance, an error of2 degrees in the detected mechanical rotor position of an SR machine,caused by a skewed sensor, a mechanical misalignment of the speed wheel,or the like, may correspond to a 0.5% decrease in efficiency of theelectric drive assembly at full load.

Although sensorless solutions also exist, conventional sensorlesscontrol schemes must implement two or more distinct processes fordifferent ranges of operating speeds or operating modes. For instance, aconventional control scheme for low speed operations, such as that ofU.S. Pat. No. 5,525,886 to Lyons, et al., may inject current signals andrefer to lookup maps to estimate the rotor position, while aconventional control scheme for high speed operations may applyobservers to phase currents to emulate and determine the rotor position.Such a need to simultaneously operate between distinct processesdepending on the speed or mode of operation can be inefficient,cumbersome and unnecessarily waste computational resources.

In addition, although the lookup tables or maps used during low speedprocesses can quickly output the rotor position based on injectedcurrent signals, the accuracy of the rotor position at the output isonly as good as the quality of the current signal that is read at theinput. More specifically, because lookup tables or maps are not capableof sufficiently filtering out noise or distinguishing errors induced bynoise from the targeted signal, the rotor position ultimately output canbe based on noise-induced errors and thus susceptible to inaccuracies.Furthermore, while conventional systems typically derive rotor speedbased on the rotor position, derivations or calculations based on noisyrotor position information can further compound noise-induced errors,output even noisier rotor speed information, and adversely impact theoverall performance of the associated SR machine.

Accordingly, there is a need to provide control schemes for controllingSR machines that are not only less costly and easier to implement, butalso more efficiently performed without compromising overallreliability. Moreover, there is a need to provide a simplified controlsystem or a single unified control scheme that can operate across widerranges of operating speeds or operating modes of an SR machine andconsume less of the computational resources allocated for use with theSR machine. There is also a need to provide a solution that is morereliable and robust to noise, all without requiring additionalcomputational resources or proximity sensors. The systems and methodsdisclosed herein are directed at addressing one or more of theaforenoted needs.

SUMMARY OF THE DISCLOSURE

In one aspect of the present disclosure, a control system for a switchedreluctance (SR) machine having a rotor and a stator is provided. Thecontrol system may include a converter circuit in electricalcommunication between the stator and a common bus, and a controllerconfigured to monitor a bus voltage of the converter circuit and a phasecurrent of the SR machine. The controller may include at least a phasevoltage estimator module configured to determine a phase voltage basedon one or more of main pulses and any diagnostic pulses, a fluxestimator module configured to determine an estimated flux based on thephase voltage and an associated mutual voltage, a position observermodule configured to determine a rotor position based at least partiallyon the estimated flux, and a main pulse control module configured tocontrol the SR machine based on the rotor position and a desired torque.

In another aspect of the present disclosure, an electric drive isprovided. The electric drive may include an SR machine having a statorand a rotor rotatably disposed relative to the stator, a convertercircuit configured to electrically communicate with the stator and acommon bus, and a controller in electrical communication with at leastthe converter circuit. The controller may be configured to monitor a busvoltage of the common bus and a phase current of the SR machine, receivemain pulses and any diagnostic pulses, determine a phase voltage basedon one of the main pulses and the diagnostic pulses, determine anestimated flux based on the phase voltage and an associated mutualvoltage, engage a position observer to determine a rotor position basedat least partially on the estimated flux, and control the SR machinebased on the rotor position and a desired torque.

In yet another aspect of the present disclosure, a method fordetermining rotor position of an SR machine being operated through aconverter circuit is provided. The method may include monitoring a busvoltage of the converter circuit and a phase current of the SR machine;receiving main pulses and any diagnostic pulses; determining a phasevoltage based on one of the main pulses and the diagnostic pulses;determining an estimated flux based on the phase voltage and anassociated mutual voltage; engaging a position observer to determine arotor position of the SR machine based at least partially on theestimated flux; and controlling an output torque of the SR machine basedon the rotor position and a desired torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of one exemplary embodiment of an electricdrive with a control system for controlling a switched reluctance (SR)machine in accordance with the teachings of the present disclosure;

FIG. 2 is a diagrammatic view of one exemplary embodiment of a controlscheme to be implemented by a controller for operating an SR machine;and

FIG. 3 is a flow diagram of one exemplary method for determining therotor position and rotor speed of an SR machine.

DETAILED DESCRIPTION

Referring to FIG. 1, one exemplary electric drive 100 that may beemployed to communicate power between a primary power source 102 and oneor more electrical loads 104 is schematically illustrated. The primarypower source 102 may include a diesel engine, a gasoline engine, anatural gas engine, or any other source of mechanical or rotationalenergy commonly used in association with mobile tools, industrialmachines, and the like. The primary power source 102 may alternativelyinclude power sources commonly used in conjunction with stationaryapplications, such as windmills, hydro-electric dams, batteries, fuelcells, or any other suitable source of energy. The electrical loads 104may include one or more devices or components which consume and/oremploy electrical power provided thereto by the electric drive 100. Forexample, with respect to industrial work machines or mobile workvehicles, the electrical loads 104 may include one or more motors foroperating tools of the machine and/or one or more traction motors forcausing motion of the associated vehicle.

Mechanical energy that is supplied by the primary power source 102 maybe converted into electrical power by the electric drive 100 for use bythe connected electrical loads 104. Conversely, any electrical powerthat may be supplied by the electrical loads 104 and/or the electricdrive 100 may be supplied to drive mechanical power to the primary powersource 102. As shown in the particular embodiment of FIG. 1, forinstance, the electric drive 100 may communicate with the primary powersource 102 through a switched reluctance (SR) machine 106, or the like.As is well known in the art, the SR machine 106 may include a rotor 110that is rotatably disposed within a fixed stator 112. The rotor 110 ofthe SR machine 106 may be rigidly and rotatably coupled to an output ofthe primary power source 102 via a coupling 108, or in otherembodiments, via a direct crankshaft, a gear train, a hydraulic circuit,or the like. Each phase or phase winding of the stator 112 of the SRmachine 106 may be electrically coupled to a common bus 114 of theelectric drive 100 via a converter circuit 116.

During a generating mode of operation, as the rotor 110 of the SRmachine 106 is rotated within the stator 112 by the primary power source102, electrical current may be induced within the stator 112 andsupplied to the converter circuit 116. The converter circuit 116 may inturn convert the electrical signals into the appropriate direct current(DC) voltage for distribution to the electrical load 104 and/or anyother device via the common bus 114. The common bus 114 may provideterminals 118, such as positive and negative or ground lines, acrosswhich the common bus 114 may communicate a bus voltage or DC linkvoltage between one or more electrically parallel devices of theelectric drive assembly 100. The electrical loads 104 may includecircuitry for converting the DC voltage supplied by the convertercircuit 116 into the appropriate electrical signals for operating anyone or more devices associated with the electric drive 100.Additionally, during a motoring mode of operation, or when theelectrical loads 104 become the sink of electrical power, the SR machine106 may be enabled to cause rotation of the rotor 110 in response toelectrical signals that are provided to the stator 112 from the commonbus 114.

As shown in FIG. 1, the converter circuit 116 may include a series oftransistors or gated switches 120 and diodes 122 for selectivelyenabling one or more phase windings or phases of the SR machine 106. Athree-phase SR machine 106, for example, may be driven using a convertercircuit 116 with six switches 120 and six diodes 122 for selectivelyenabling or disabling each of the three phases of the SR machine 106.Each of the switches 120 may further be enabled or disabled via gatesignals while an external or secondary power source 124 provides poweracross the positive and negative lines 118 of the common bus 114 toforce current through the respectively enabled switches 120 and diodes122. The electric drive 100 may also be provided with an exemplarycontrol system 126 configured to, among other things, determine theposition of the rotor 110 of the SR machine 106 relative to the stator112 and control operation of the SR machine 106 based on the determinedrotor position.

As illustrated in FIG. 1, the control system 126 may generally includethe converter circuit 116, at least one controller 128 in communicationwith the gated switches 120 of the converter circuit 116, as well as amemory 130 in communication with the controller 128 that is providedwithin and/or external to the controller 128. More particularly, thecontroller 128 may be electrically coupled to the switches 120 in amanner which enables the controller 128 to selectively engage theswitches 120 and source current through the different phases of the SRmachine 106, as well as in a manner which enables the controller 128 tomonitor electrical characteristics of the SR machine 106 and the bus orDC link voltage of the common bus 114 during operation of the SR machine106. The memory 130 may retrievably store one or more algorithms,machine data, predefined relationships between different machineparameters, preprogrammed models, such as in the form of lookup tablesand/or maps, or any other information that may be accessed by thecontroller 128 and relevant to the operation of the SR machine 106.

The controller 128 of FIG. 1 may be implemented using one or more of aprocessor, a microprocessor, a microcontroller, a digital signalprocessor (DSP), a field-programmable gate array (FPGA), an electroniccontrol module (ECM), an electronic control unit (ECU), or any othersuitable means for electronically controlling functionality of thecontrol system 126. The controller 128 may be configured to operateaccording to predetermined algorithms or sets of instructions foroperating the electric drive 100 and the SR machine 106 based on therotational speed and/or position of the rotor 110 relative to the stator112 or other operating characteristics of the electric drive 100. Suchalgorithms or sets of instructions may be preprogrammed or incorporatedinto memory 130 that is associated with or at least accessible to thecontroller 128 as is commonly used in the art. Moreover, the algorithmsor instructions implemented by the controller 128 may be categorizedinto modular arrangements such as that schematically shown for examplein FIG. 2.

As shown in FIG. 2, the controller 128 may be configured to include aspeed control module 132, a torque control module 134 and a main pulsecontrol module 136, combinations of which are often employed inconventional SR machine controls. Specifically, the speed control module132 may be configured to determine the desired or target speed of the SRmachine 106 based on any combination of operator input, machine inputparameters or constraints, automated controls, and the like. In turn,the torque control module 134 may be configured to determine the targetoutput torque of the SR machine 106, which corresponds to achieving thetarget speed determined by the speed control module 132. The main pulsecontrol module 136 may be configured to generate or use the switchingcommand, or the sequence of pulses or current signals designed toselectively enable the switches 120 of the converter circuit 116, tooperate the SR machine 106 according to the target output torque orspeed.

While the main pulse control module 136 may be suited for use with highspeed operating modes or relatively high operating speeds of the SRmachine 106, low speed operating modes or relatively low operatingspeeds of the SR machine 106 may be managed by a diagnostic pulsecontrol module 138 as shown in FIG. 2. In particular, high speedoperating modes may involve operating speeds that are higher than orinclusive of a nominal or base speed, while low speed operating modesmay involve operating speeds that are zero or lower than the base speed.Although base speeds may vary per application, base speeds can generallybe defined as the maximum speed at which the SR machine 106 is able tooutput constant torque and before torque output begins to decreaseproportionally in relation to the operating speed.

Still referring to FIG. 2, the diagnostic pulse control module 138 ofthe controller 128 may be disposed in parallel to the main pulse controlmodule 136. The diagnostic pulse control module 138 may be configured togenerate and inject diagnostic or test pulses into each idle phase ofthe stator 112 or phases that are not controlling the SR machine 106 ata given instance. Moreover, the diagnostic pulses may selectively enablethe corresponding switches 120 of the converter circuit 116 and drive aphase current with a substantially constant current height through eachidle phase of the stator 112, so as to facilitate computations to beperformed later. Furthermore, the diagnostic pulse control module 138may be configured to generate and inject the test pulse into idle phasesaccording to the most recently assessed or estimated rotor position.

As demonstrated by the architecture of the controller 128 in FIG. 2,processes that are applied to either the main pulses or the diagnosticpulses are streamlined into a single algorithm or sequence ofinstructions. Moreover, the entire range of operating speeds of the SRmachine 106, for instance, both high speed and low speed operatingmodes, which previously required two or more distinct algorithms orprocess groups, may be managed by the unified algorithm or set ofprocesses of FIG. 2 to not only reduce complexity, but also to sparesignificant computational resources. For example, either the main pulseduring relatively high speed operations, or the diagnostic pulse duringrelatively low speed operations can be processed by the controller 128in substantially the same manner to assess rotor position and/or rotorspeed. At even higher or very high speeds, the main pulse control module136 will likely shift between a discontinuous conduction mode (DCM) anda continuous conduction current mode (CCM) to satisfy certain powerrequirements. Based on the sensorless architecture and techniquesdisclosed herein, rotor position and speed estimation may also bepossible at such high speeds and during CCM modes of operation.

To determine rotor position or rotor speed, the controller 128 of FIG. 2may initially provide a phase voltage estimator module 140 configured todetermine the voltage of the phase or phase voltage based on either themain pulse or the diagnostic pulse and known electrical propertiesbetween phase voltage and phase current for the given SR machine 106.The controller 128 may further include a mutual voltage estimator module142 configured to determine the associated mutual voltage, for instance,with reference to one or more preprogrammed lookup tables, maps, or thelike, which predefine relationships between mutual voltage values, phasecurrent values, estimated rotor position values, and the like.Furthermore, the controller 128 may apply the phase voltage and themutual voltage, and any suitable calculation, computation, derivationand/or manipulation thereof, as inputs to a position observer module 144to determine rotor position and to a speed observer module 146 todetermine rotor speed as shown in FIG. 2.

While other manipulations or derivations based on the phase voltage andthe mutual voltage will be apparent to those of skill in the relevantart, the controller 128 of FIG. 2 may provide a flux estimator module148 configured to determine an estimated flux based on the phase voltageand the mutual voltage. For example, the flux estimator module 148 mayuse known electrical properties to determine a total flux based on thedetermined phase voltage and to determine a mutual flux based on thedetermined mutual voltage. The flux estimator module 148 may thencalculate the estimated flux based on a difference between the totalflux and the mutual flux. As shown, the controller 128 may furtheremploy a current estimator module 150 which determines an estimatedphase current based on the estimated flux, and a current error synthesismodule 152 which determines the error between the estimated phasecurrent and one or more phase currents of the SR machine 106. Thecurrent error may then be fed into each of the position observer module144 and the speed observer module 146 to determine the rotor positionand the rotor speed, respectively.

The position observer module 144 of FIG. 2 may employ a state observersystem which emulates the internal state of a real system, as well asreceives input parameters and generates output parameters much like areal system. In the present case, the position observer module 144 maybe configured to at least partially emulate a real SR machine 106,receive current error as input, and generate rotor position as output.While the position observer module 144 shown in FIG. 2 may be configuredto determine rotor position based on current error, it will beunderstood that the position observer module 144 may be modified todetermine rotor position using other inputs, such as the phase voltage,mutual voltage, estimated flux, phase current, or any other suitableparameter adapted by the controller 128. Optionally, the controller 128may also provide a position processing module 154 configured to processthe output of the position observer module 144 as needed to furtherrefine and/or calibrate the estimated rotor position.

Similar to the position observer module 144, the speed observer module146 may employ a state observer system to at least partially emulate theinternal state of a real SR machine 106, receive current error as input,and generate rotor speed as output. Additionally, although the speedobserver module 146 may be configured to determine rotor speed based oncurrent error, the speed observer module 146 may be modified to employother inputs, such as the phase voltage, mutual voltage, estimated flux,phase current, or any other suitable parameter adapted by the controller128 to assess rotor speed. In other modifications, the speed observermodule 146 may be omitted entirely, and derivations of the rotorposition with respect to time may be used to determine rotor speed.However, it will be understood that such indirect estimations of rotorspeed may magnify any noise or other errors untreated by the positionobserver module 144. Furthermore, the controller 128 may optionallyinclude a speed processing module 156 configured to process the outputof the speed observer module 146 as needed to further refine and/orcalibrate the estimated rotor speed.

INDUSTRIAL APPLICABILITY

In general, the foregoing disclosure finds utility in variousapplications relating to switched reluctance (SR) machines or any othersuitable electric machine being employed as a motor and/or generator. Inparticular, the disclosed systems and methods may be used to providemore efficient control of SR machines that are typically employed inassociation with the electric drives of power generation machines,industrial work vehicles, and other types of machines commonly used inthe art. The present disclosure may also be implemented with othervariable-speed drives commonly used in association with industrial andconsumer product applications. The present disclosure may further beused with integrated starters, generators, or the like, commonlyassociated with automotive, aerospace, and other comparable mobileapplications.

One exemplary algorithm or controller-implemented method 158 foroperating an SR machine 106 is diagrammatically provided in FIG. 3. Asshown in block 158-1, the controller 128 may initially be configured tomonitor the bus voltage or the DC link voltage of the common bus 114and/or the converter circuit 116 associated therewith, as well as thephase current of the SR machine 106. The controller 128 per block 158-2may further be configured to generate or use main phase current pulses,such as via the main pulse control module 136 of FIG. 2, for example, inaccordance with a switching command designed to selectively enableswitches 120 of the converter circuit 116 to operate the SR machine 106according to a desired or target speed or torque. Furthermore, duringlow speed operations, the controller 128 according to block 158-3 may beconfigured to generate diagnostic pulses, such as via the diagnosticpulse control module 138 of FIG. 2. More specifically, the diagnosticpulses may be generated and injected into each idle phase of the stator112 and designed to selectively enable the corresponding switches 120 ofthe converter circuit 116.

Additionally, the controller 128 according to block 158-4 of FIG. 3, maybe configured receive either the main pulses or the diagnostic pulsessuch as via the phase voltage estimator module 140 of FIG. 2. Moreparticularly, the controller 128 may accept the main pulses or thediagnostic pulses without discrimination and without regard to theoperating mode or speed of the SR machine 106. Furthermore, thecontroller 128, such as via the phase voltage estimator module 140, maythen be configured to determine the phase voltage associated with thereceived pulses according to block 158-5. The controller 128, such asvia the flux estimator module 148 of FIG. 2, may additionally beconfigured to determine an estimated flux based at least partially onthe phase voltage in block 158-6. In one example, the flux estimatormodule 148 may compute a total flux based on the determined phasevoltage, compute a mutual flux based on a mutual voltage associated withthe received pulse, and ultimately calculate the estimated flux as thedifference between the total flux and the mutual flux. In alternativeembodiments, the controller 128 may determine the estimated flux usingother techniques known in the art.

Still referring to FIG. 3, the controller 128 may further be configuredto engage a position observer, such as with the position observer module144 of FIG. 2, to determine the rotor position based on the estimatedflux according to block 158-7. As described with respect to FIG. 2, thecontroller 128 may determine an estimated phase current based on theestimated flux, determine the error between the estimated phase currentand one or more phase currents of the SR machine 106, and use thecurrent error as an input to the position observer to output theestimated rotor position. In other embodiments, the controller 128and/or the position observer may employ any one of a variety of othertechniques to similarly derive the estimated rotor position directly orindirectly from the estimated flux. In still further modifications, thecontroller 128 and/or the position observer in block 158-7 may derivethe estimated rotor position based on parameters other than theestimated flux, such as the phase voltage, mutual voltage, phasecurrent, and the like.

Furthermore, the controller 128 may be configured to engage a speedobserver, such as with the speed observer module 146 in FIG. 2, todetermine the rotor speed based on the estimated flux according to block158-8. Similar to block 158-7, the controller 128 in block 158-8 may usethe speed observer to emulate a real SR machine 106 and to estimate therotor speed based on current error. The controller 128 and/or the speedobserver may alternatively employ other techniques to arrive at theestimated rotor speed. In addition, as illustrated in FIG. 3, thecontroller 128 may also be configured to perform the functions of block158-8 in parallel with or independently of those of block 158-7, so asto minimize any spread of corrupted data between the position observerand the speed observer. The controller 128 in block 158-9 mayadditionally perform any post-processing that may be needed to furtherrefine and/or calibrate the estimated rotor position and/or rotor speed.Still further, the controller 128 in block 158-10 may be configured tocontrol the SR machine 106 based on the estimated rotor position and/orthe estimated rotor speed, as well as based on the desired torque and/orspeed of the SR machine 106.

Based on the foregoing, the present disclosure provides a simplified andyet robust solution for operating an SR machine across a much widerrange of operating speeds. More particularly, the present disclosureprovides a control architecture which streamlines the processes used fordetermining the rotor position of an SR machine to conservecomputational resources and excess costs associated therewith. Thepresent disclosure also employs independent position and speed observerswhich naturally filter and/or correct for noise-induced errors toprovide for more reliable results. The present disclosure therebyprovides a sensorless solution that eliminates the need for costlyposition or proximity sensors without compromising performance. It willbe appreciated that while only certain embodiments have been set forthfor the purposes of illustration, alternatives and modifications will beapparent from the above description to those skilled in the art. Theseand other alternatives are considered equivalents and within the spiritand scope of this disclosure and the appended claims.

What is claimed is:
 1. A control system for a switched reluctance (SR)machine having a rotor and a stator, comprising: a converter circuit inelectrical communication between the stator and a common bus; and acontroller configured to monitor a bus voltage of the converter circuitand a phase current of the SR machine, the controller having at least aphase voltage estimator module configured to determine a phase voltagebased on one or more of main pulses and any diagnostic pulses, a fluxestimator module configured to determine an estimated flux based on thephase voltage and an associated mutual voltage, a position observermodule configured to determine a rotor position based at least partiallyon the estimated flux, and a main pulse control module configured tocontrol the SR machine based on the rotor position and a desired torque.2. The control system of claim 1, wherein the controller furtherincludes a speed observer module configured to determine a rotor speedbased at least partially on the estimated flux.
 3. The control system ofclaim 1, wherein the phase voltage estimator module is configured todetermine a phase voltage based on one or more of the main pulses duringhigh speed operating modes and any of the diagnostic pulses during lowspeed operating modes.
 4. The control system of claim 1, wherein thecontroller further includes a mutual voltage estimator module configuredto determine the mutual voltage by referring to one or morepreprogrammed maps defining relationships between mutual voltage values,phase current values, and estimated rotor position values.
 5. Thecontrol system of claim 1, wherein the controller further includes acurrent estimator module configured to determine an estimated currentbased on the estimated flux, and a current error synthesis moduleconfigured to determine a current error based on a comparison betweenthe estimated current and one or more phase currents of the SR machine.6. The control system of claim 5, wherein the position observer moduleis configured to determine the rotor position based at least partiallyon the current error, the controller further including a speed observermodule configured to determine a rotor speed based at least partially onthe current error.
 7. The control system of claim 1, wherein thecontroller further includes a diagnostic pulse control module configuredto inject the diagnostic pulses during low speed operating modes.
 8. Thecontrol system of claim 7, wherein the controller is configured toprocess both of the main pulses and the diagnostic pulses, and theposition observer module is configured to determine rotor position forboth high speed operating modes and low speed operating modes.
 9. Anelectric drive, comprising: a switched reluctance (SR) machine having astator and a rotor rotatably disposed relative to the stator; aconverter circuit configured to electrically communicate with the statorand a common bus; and a controller in electrical communication with atleast the converter circuit, the controller being configured to monitora bus voltage of the converter circuit and a phase current of the SRmachine, receive main pulses and any diagnostic pulses, determine aphase voltage based on one of the main pulses and the diagnostic pulses,determine an estimated flux based on the phase voltage and an associatedmutual voltage, engage a position observer to determine a rotor positionbased at least partially on the estimated flux, and control the SRmachine based on the rotor position and a desired torque.
 10. Theelectric drive of claim 9, wherein the controller is further configuredto determine a rotor speed based at least partially on the estimatedflux.
 11. The electric drive of claim 9, wherein the controller isconfigured to determine a phase voltage based on one or more of the mainpulses during high speed operating modes and any of the diagnosticpulses during low speed operating modes.
 12. The electric drive of claim9, wherein the controller is configured to determine the mutual voltageby referring to one or more preprogrammed maps defining relationshipsbetween mutual voltage values, phase current values, and estimated rotorposition values.
 13. The electric drive of claim 9, wherein thecontroller is further configured to determine an estimated current basedon the estimated flux, determine a current error based on a comparisonbetween the estimated current and one or more phase currents of the SRmachine, and determine the rotor position and a rotor speed based atleast partially on the current error.
 14. A method for determining rotorposition of a switched reluctance (SR) machine being operated through aconverter circuit, comprising: monitoring a bus voltage of the convertercircuit and a phase current of the SR machine; receiving main pulses andany diagnostic pulses; determining a phase voltage based on one of themain pulses and the diagnostic pulses; determining an estimated fluxbased on the phase voltage and an associated mutual voltage; engaging aposition observer to determine a rotor position of the SR machine basedat least partially on the estimated flux; and controlling an outputtorque of the SR machine based on the rotor position and a desiredtorque.
 15. The method of claim 14, further determining a rotor speedbased at least partially on the estimated flux.
 16. The method of claim14, wherein the main pulses are received during high speed operatingmodes and the diagnostic pulses are received during low speed operatingmodes.
 17. The method of claim 14, wherein the mutual voltage isdetermined by referring to one or more preprogrammed maps definingrelationships between mutual voltage values, phase current values, andestimated rotor position values.
 18. The method of claim 14, furtherdetermining an estimated current based on the estimated flux, anddetermining a current error based on a comparison between the estimatedcurrent and one or more phase currents of the SR machine.
 19. The methodof claim 18, wherein the rotor position is determined based at leastpartially on the current error, and a rotor speed is determined based atleast partially on the current error.
 20. The method of claim 14,further injecting the diagnostic pulses during low speed operatingmodes, the rotor position for both high speed operating modes and lowspeed operating modes are determined by the position observer.